Shotgun Tube Having Gain Twist Rifling

ABSTRACT

This invention relates to a shotgun tube, either an inserted/attached short section that replaces a conventional choice device, or one that forms an integral section of the shotgun barrel. It is designed to provide major advances in two performance features of shotguns: (1) It provides an extremely uniform expanded shot pattern at short ranges 10 to 20 feet and (2) it provides rotational stabilization for both rifled slugs and sabot encased sub-caliber projectiles that significantly improves accuracy at longer ranges.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

This invention relates to a shotgun tube, either an inserted/attached short section that replaces a conventional choke device or one that forms an integral section of the shotgun barrel. It is designed to provide major advances in two performance features of shotguns: (1) It provides an extremely uniform expanded shot pattern at short ranges 10 to 20 feet and (2) it provides rotational stabilization for both rifled slugs and sabot encased suo-caliber projectiles that significantly improves accuracy.

2. Discussion of the Prior Art

There have been numerous patents that bear on the subject of improving the performance of shotguns especially in improvement/modification of spread pattern of the shot charge. Most patents are directed to choke tubes that are short cylindrical tubes with different internal diameters, or chokes, on the shotgun muzzle region. Hence the generic designation of the “choke” of the shotgun being “full” for large constrictions and “modified” and “cylinder” etc., as the constriction is eased.

An early patent for a changeable choke device is U.S. Pat. No. 2,098,617 issued to R. M. Cutts and titled “Spreader Tube”. It describes the famous “Cutts Compensator” set of variable chokes. It is not a rifled type of choke.

U.S. Pat. No. 8,458,945, U.S. Pat. No. 8,276,305, and U.S. Pat. No. 7,523,581, propose to use types of propellant gas bypass devices to interrupt the shot column. Their efficacy has not been otherwise documented.

U.S. Pat. No. 4,711,048 and U.S. Pat. No. 3,492,750 relate to muzzle attachments that provide a very large short constriction at the shotgun muzzle, which would impart a significant inward component to the shot column as it exits the muzzle. This inward velocity should then provide a spreading component and result is larger shot spreading. Again, the efficacy of this approach has not been documented.

U.S. Pat. No. 4,071,971 describes a method of rifling a removable choke tube at a small fixed angle of about 4 degrees with respect to the bore axis. This is proposed to provide a pattern at distances relative to skeet shooting, about 30 yards or 90 feet. The patent also applies to rifling of the final 4 inches or so of the complete shotgun barrel.

U.S. Pat. No. 2,484,988 uses a very short, less than one inch, angled rifled section at the muzzle end of one embodiment of a set of devices for controlling the shot pattern of a shotgun. Again, the rifling is of constant twist and is slanted at an undefined small angle relative to the device bore.

Both patents that use rifling near the muzzle make no mention of the shot charge being encased in a plastic shot cup. Since all current shotgun shells use such a shot cup, our gain twist rifling is designed to be effective in spreading the shot pattern from shells that have a plastic shot cup.

None of the patents cited here claim to produce uniform, expanded patterns of shot at short ranges (10-20 feet) and stabilize slugs, to improve accuracy at longer ranges (75-100 yds.),

SUMMARY OF THE INVENTION

Twist is the descriptor that describes the rate at which the rifling of the barrel of a weapon rotates along the barrel length, it is conventionally described as the length along the barrel in inches that causes a full rotation (360 degrees) of the projectile. The “twist” is then, for example, “1 in 9 or 1/9” for such a rifling twist that completes a complete 360 degree revolution in 9 inches of travel along the length of the barrel. Conventionally, the twist remains constant along the barrel length for almost all firearms.

“Gain-twist” describes the situation where the twist becomes more sloped relative to the barrel bore as the distance along the bore goes from breech to muzzle. That is, when the twist at the chamber end is, for example, 1 in 12 and it changes smoothly to become 1 in 9 at the muzzle. Alternatively the description could be that the angular slope of the rifling at the chamber has a given value and the slope at the muzzle has a larger value.

We have applied this concept to produce a shotgun tube that has a rifling slope significantly less than one degree at the chamber end of the tube. This value changes smoothly and consistently to a value as large as 30 degrees or more at the muzzle end of the tube. This already designed and fabricated shotgun tube is a screw-in type and has an overall length of about 4 inches.

Test firing of a shotgun having one of these devices confirms that short-range (10 feet) patterns that are very uniform with diameters of 15 plus inches can readily be achieved. Similarly, patterns of smaller and larger diameters have been derived from variations in the tube fabrication with various exit angles for the gain twist.

This device can be made in shotgun gages, 410/20/16/12/10 and to fit shotgun barrels that are threaded to accept industry standard screw-in chokes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A An illustration of the device with serrated end.

FIG. 1B An illustration of the device without serrated end.

FIG. 1C An end view of device with serrations and radial rifling.

FIG. 1D An end view of device with radial rifling and no serrations.

FIG. 2 An illustration of “Gain Twist” rifling.

FIG. 3A An end view of rifling with flat grooves and lands.

FIG. 3B An end view of rifling with radial grooves and sharp pointed “lands”.

DETAILED DESCRIPTION OF THE INVENTION

“Gain Twist” describes the situation where the twist becomes more sloped relative to the barrel bore as the distance along the bore goes from breech to muzzle. That is, when the twist at the chamber end is, for example, 1 in 12 and it changes smoothly to become 1 in 9 at the muzzle. Alternatively the description could be that the angular slope of the rifling at the chamber end has a given value and the slope at the muzzle has a larger value.

The gain twist rifling of this invention is shown in FIG. 2, [200]. The slope of the rifling with respect to the tube bore axis increases as the distance along the bore increases from the chamber end [202] to the muzzle end [204]. The dotted line straight line [208] illustrates the non-linear character of the gain twist rifling. Such a variable is readily programmed into a computer numerically controlled (CNC) lathe or milling machine, thus simplifying the production of such a device.

This slope is programmed as a quadratic equation (an algebraic function dependent on the square of the length along the bore of the tube from the chamber end) of groove offset from the starting point at the chamber end of the tube as the length along the bore axis increases. Such a function provides a smooth and repeatable increasing groove slope angle [206] along the bore axis.

Other functionality of the gain twist rifling can readily be used for this purpose.

FIG. 3a and FIG. 3b illustrate the type of rifling that is used here. FIG. 3a [302] shows a section of tube with both lands [304] and grooves [306], both of which have flat surfaces. In this type of rifling there are 12 lands and 12 grooves around the tube inner diameter. The number of lands and grooves can be as small as 2 or as large as 24. The depth of each groove is about 0.010 inches deep. Generally the width of grooves and the width of lands are equal, although this convention is not universal, and this invention functions with unequal groove and land widths.

FIG. 3b [320] illustrates a second type of rifling that has been demonstrated. In this case the grooves are cut in the form of a circular configuration with a radius of approximately 0.125 inches and forms circular grooves [322] that are again about 0.010 inches deep. They are cut so that the lands [324] form a sharp edge and have essentially zero width.

Tubes of both groove types formed with an exit groove angle at the muzzle end [204] of 30 degrees has produced an extremely uniform pattern of some 20 inches diameter incident on a paper target at a distance of 20 feet when #4 shot, #6 shot or #4 buckshot was tested. Tests with 00 buckshot showed a hollow ring pattern that is undoubtedly caused by the small number of pellets in the shell (9 pellets). All tests were performed using shotgun shells that have a plastic shot cup encasing the shot charge.

HOW TO USE THE INVENTION

Similar results would be obtained if this type of gain twist rifling were to be fabricated as manufactured for shotgun barrels directly rather than as a screw-in removable tube.

Tubes with 6 degree, 12 degree, 20 degree and 30 degree exit rifling slope were fabricated and tested. This illustrates that such a gain twist tube can be designed and fabricated to match any dispersion pattern that is desired for specific uses, such as optimized for skeet shooting from specific stations, etc.

A second benefit that is derived from the gain twist tube is that shotgun slugs are better stabilized when fired, using the gain twist tube. Both conventional rifled slugs and sabot mounted sub-caliber projectiles demonstrated improved accuracy and grouping characteristics as compared to either smooth bored shotguns or with conventional slug filing rifled shotguns.

This invention is designed to be effective in close range home defense. Military and police should find this device useful in room clearing maneuvers and fast moving targets.

When serrations consisting of 8 slots approximately 0.300 inch deep×60 degrees included angle are cut across the muzzle end of this device creates very sharp points, which are useful for breeching doors, windows etc., and is a very effective hand to hand combat weapon.

BEST MODE OF THE INVENTION

FIG. 1B represents the best mode of the invention contemplated by the inventor for carrying out the invention. 

What is claimed is:
 1. A shotgun barrel comprising: a screw-in device that mates to industry-standard threads for installation of standard chokes; said screw-in device having a nominal rifled length of about 4 inches; and said screw-in device having a slope of the rifling twist that starts at the chamber end of the unit with a low angular twist, typically near to zero degrees.
 2. A shotgun barrel according to claim 1, wherein the slope of the rifling twist increases continually toward the muzzle end of the barrel.
 3. A shotgun barrel according to claim 1, wherein the final rifling slope at the muzzle end of the barrel can be made to be any desired larger angle, of about 30 degrees.
 4. A shotgun barrel according to claim 1, wherein the groove depth of such gain twist rifling is about 0.010 inches.
 5. A shotgun barrel according to claim 1, wherein the groove width of such gain twist rifling is about 0.125 inches.
 6. A shotgun barrel according to claim 1, wherein the land width of such gain twist rifling is about 0.125 inches.
 7. A shotgun barrel according to claim 1, wherein the device can be secured to the muzzle end of a shotgun by soldering.
 8. A shotgun barrel according to claim 1, wherein the device can be secured to the muzzle end of a shotgun by clamping.
 9. A shotgun barrel according to claim 1, Wherein the grooves and lands of the gain twist rifling are designed to function properly with shotgun shells having a plastic shot cup.
 10. A shotgun barrel according to claim 1, wherein the grooves and lands of the gain twist rifling are designed to stabilize and improve long range accuracy of rifled slugs and saboted sub-caliber slugs. 